The chiropractic profession began in the US in the late 1800s when the US was a developing nation. This was a rugged era when new American settlers pushed the boundaries of the US in a westerly direction from the colonial Eastern states toward California. These were the days of the “Wild West” from which the iconic images of cowboys and frontiersmen emerged during this dangerous and exciting period of expansion. At this time, many Americans became disillusioned with the rapid industrialization of the eastern part of the country from the late 1800s through the turn of the century. These Americans felt that times were better during when people were more in tune with the land.Thus, they advocated for a return to simpler times that involved rural living and the philosophical perspectives that came with it [1] .
However, at this time medicine was increasingly turning to large cities to locate large medical institutions and hospitals, not only in which to care for patients, but to train medical students [2] . Medical care during these times was limited and based greatly on practices passed down from one generation of doctors to the next. For context, the germ theory of disease, antisepsis, and many other standard medical practices had not been discovered.Medical science was crude and little research existed to validate medical procedures. In fact,the randomized controlled trial research design did not become used to test the effectiveness of various medical therapies until the 1900 [3] . In the late 1800s and early 1900s, there were no standards or accreditation procedures in medical education. Thus, at that time, American medical education was essentially proprietary in nature,a fact criticized by many physicians.
Various medical cures were often harsh and some critics suggested that patients survived medical therapies, rather than disease [4] . Given the lack of knowledge related to bacteriology or other infectious diseases,there were virtually no effective interventions for infection. Medical doctors of the period relied greatly upon the practice of heroic medicine [5] . Heroic medicine involved the draining of blood from sick patients, the use of purgatives, administration of mercury, and other treatments that are now known to be fatal [4,6] . Early American physicians had virtually no treatments in their therapeutic armamentarium for common disorders of the muscles, bones,and joints, particularly of the spine.
In this nearly unregulated environment, in 1847, a group of medical doctors, who called themselves regular or orthodox doctors, created the American Medical Association (AMA) [7] .The goal of the AMA was to control the healthcare industry and protect the benefits of its members. Thus, the AMA was againstnon regular healthcare providers and created a code of ethics deeming non-regulars as anti-scientific and that any AMA member who collaborated with a non-regular committed a breach of the code and would be sanctioned [8] .
Due to the harsh nature of the medical treatments, people often sought the care of the non-regular providers, who also were known as alternative providers of health care [9] . Alternative healthcare practitioners were abundant in the 1800s. Because alternative practitioners offered conservative, and often less damaging, healing treatments, they might have seen positive results where orthodox heroic medicine practitioners did not. Alternative providers used natural healing agents such as diet changes, herbs and plants, exercise, bonesetting, manipulation,religious healing, magnetic healing, sunshine therapy, and baths. The most commonly known professions that arose towards the end of the century included homeopathy, osteopathy,naturopathy, and chiropractic [5] .
It is important to understand the evolution of health professions that were contemporary with the begging of chiropractic in order to place the emergence of chiropractic into perspective. This section provides an overview of the common alternatives to emerge in the US.
Thomsonism,founded by Samuel Thomson around 1800s, was considered the first medical alternative in the US [10] . Thomsonism was an herbal remedy system. Thomson’s goal was to provide the herbal remedies in a simple form so that the common layperson could prepare them and administer them to those who were ill [10] . This was considered to be safer than receiving heroic medicine offered by the orthodox physicians [11] . Thomsonism was popular amongst Americans. The Thomsonism movement was fragmented due to dissenting views from within pertaining to the fundamental practices of Thomsonism. One faction, the eclectics, believed that formal education was required to practice Thomsonism. This group formed several eclectic medical schools in the US. These alternative medical schools persevered until the late 1930s when they were closed due to pressures from the AMA [5] .
Homeopathy, a popular early alternative to orthodox medicine, was developed by Samuel Hahnemann, a German physician, who found orthodox medical cures unsuccessful and dangerous [12] . Hahnemann believed that diseases could be cured by using extremely dilute herbal remedies by producing symptoms similar to the disease [13] . Homeopathy was brought to the US in 1825 by Hans Gram after he received medical training in Europe [12] . The American public found homeopathy attractive because many homeopaths were trained in orthodox medical schools; yet, homeopathic methods were less intimidating and appeared more scientific than heroic medicine [12] . The number of homeopaths was large and they were successful in creating their own homeopathic medical schools and hospitals. Most American orthodox practitioners did not accept homeopathy and labelled it quackery [13] . This was probably compounded by many American MDs who perceived homeopathy as a threat to their business [7] .Homeopaths also created the word “allopath”for the orthodox practitioners. Allopath means to treat disease by inducing a pathological reaction that is antagonistic to the one being treated [6] .Relationships between homeopaths and allopaths deteriorated, becoming a significant reason that the allopaths formed the AMA [5] .By the early 1900s, homeopathy had largely been eliminated by competition from organized medicine in the US.
Another US medical alternative, osteopathy,emerged during the 1870s [14] . Andrew Taylor Still founded osteopathy and believed that the body was a self-repairing mechanism that functioned best without impediments to the circulatory and nervous systems and that these impediments could be relieved using manual manipulation.Osteopaths manipulated joints in addition to other procedures and eventually expanded their scope of practice to include prescribing pharmaceuticals and performing surgery [14] .Despite more than 50 years of opposition by the AMA, osteopathy was eventually absorbed by orthodox medicine. Several authors have stated that in the US today, osteopathy and medicine are virtually indistinguishable in practice [5,15–16] .
It was during this time that Daniel David Palmer, an Iowan teacher, grocer, and farmer, began to develop what later became chiropractic [17] . The philosophical bases for DD’s embryonic chiropractic were spiritualism and vitalism [18–19] .Spiritualism was considered to be a belief that there was a spiritual life after death and that living people could communicate with the dead through the use of a state of trance [20] .Vitalism was a belief that living beings have a vital force, that the whole of a human is made up of more than the sum of its parts and a cause of life [20] . Vitalism served as an opposing philosophical concept to the highly mechanistic concepts of medicine and the industrial revolution. Thus, vitalism became popular in the US at the time that DD Palmer (Figure 2–1) was developing his new philosophy of chiropractic.DD Palmer believed that disease was related to the interruption of nervous impulses that influenced innate intelligence [16] . DD also believed that the body had inborn healing or homeostatic capacities [21] . This philosophy was compatible with the perspectives of rural Americans of the period [16] .
Figure 2–1 DD Palmer
DD Palmer’s early theories were that the vertebrae could become misaligned and that if the bones were manipulated this would improve the function of the circulatory and nervous systems to allow natural healing to take place [22] .Most people consider spinal manipulation, also known as spinal manipulative therapy (SMT), as the cornerstone of chiropractic treatment. Spinal manipulation has long been practiced in the world and DD Palmer acknowledged this fact.However, it was DD Palmer who claimed to develop specific spine manipulation procedures that used different parts of the vertebrae as levers. This manipulation alone was and is not chiropractic. Chiropractic consists of the use of manipulation with the hypothesis that the nervous system and other bodily functions can be improved by relieving such obstructions,known as vertebral subluxations, and then allowing the body to heal itself through its various homeostatic capacities. Thus, when a chiropractor manipulated the spine with this concept in mind, it was called a spinal adjustment.
DD Palmer did not believe that chiropractic was subservient to medicine; he stated that it was an alternative to medicine [16] . Chiropractic was in contrast to medicine. DD said, “Our healing is done entirely by the hands; there are no drugs used” [23] .
Many medical doctors left rural areas to develop practices, colleges, and hospitals in metropolitan areas. Chiropractors then began to fill the role of healthcare providers in these rural areas where the Populist movement was aligned with the philosophical ideals of chiropractic [24] .Chiropractic care became popular and common in these rural areas.
With its new philosophy and practice, as well as the attempts of the AMA to eliminate chiropractic, chiropractic was attacked by medical licensing agencies and associations.Therefore, the young chiropractic profession had to clearly identify itself as different than medicine [21] . Thus, the distinctive identity of chiropractic was based on its philosophy and art. This approach was an important part of chiropractors being able to establish their own state licensing boards over a period of decades.
Because chiropractic evolved as being separate and distinct from medicine, chiropractors fil l provider roles in a wide variety of areas as drugless care providers. Some chiropractors solely address chiropractic vertebral subluxations. Others offer care that includes rehabilitation, nutrition,or procedures for helping with internal disorders.
Similar to American medical education in the 1890s, the earliest years of chiropractic education included student observation of teachers while they cared for patients [25] . When DD Palmer’s students graduated, he printed on their diplomas that they were qualified to “teach and practice” chiropractic [26] . Thereafter, graduates opened new chiropractic schools; rivalries between schools and founders developed based upon differing opinions on chiropractic thoughts and procedures. Eventually, there became two main rivaling groups. Those chiropractors who agreed with Palmer’s assertion that chiropractic was done by hand only focused on the manual correction of vertebral misalignments and called themselves straight chiropractors [22] . The other group included other methods of healing,such as adjustive instruments, naturopathic techniques, and physiotherapeutic therapy devices, were dubbed mixers [27] .
By the early 1920s, chiropractic college curricula were 18 months or longer [28] .Chiropractic schools continued to increase entrance requirements and lengthened curricula.By the 1970s, programs were modern with ever increasing entrance requirements. Chiropractic educational programs continued to evolve to modernize entrance requirements and enhance curricula to the present day [29] . These high quality chiropractic educational programs continued to improve and met with less resistance from the AMA. The chiropractic profession was recognized by the United States Office of Education with its own programmatic accrediting agency in 1974. This agency was called the Council on Chiropractic Education(CCE) and maintains the same name today [30–31] .When the profession had its own accrediting body, chiropractic students became eligible for federal student loans [32] .
In the early years US licensing laws favored the established medical profession. Thus, the AMA lobbied strongly to continue its control over the marketplace and continued to oppose the development of chiropractic in an effort to make it subservient to organized medicine. In the states that did not legally recognize chiropractic,chiropractors were arrested and sent to jail, being accused of practicing “medicine” without a license [33–34] . Chiropractors battled many cases in court and continued to lobby for licensure in each of their respective states. Laws to govern and regulate the practice of chiropractic in the US were enacted slowly over many years and chiropractors eventually gained licensure laws in all of the states.
Even though laws were passed that allowed chiropractors to practice in their jurisdiction, organized medicine continued to oppose chiropractors. However, medicine lost the battle to prevent chiropractic from establishing licensing laws and it attempted to retard chiropractic with a new method called basic science laws. This approach involved getting laws passed in each of the states that required candidates eligible for licensure to pass prelicensure examinations on basic science topics. Medical doctors, osteopaths,and chiropractors were usually required to take these examinations. The basic science tests were mainly relevant to practicing medicine and created to keep chiropractors from obtaining eligibility for state licensure. Given the low relevance of the examinations to chiropractic practice, many chiropractors failed the tests and were unable to be licensed in their states [35] .Eventually, the chiropractic profession won the right to create its own national board examinations, which are now administered by the National Board of Chiropractic Examiners.These tests are required by most states to demonstrate that licensees meet the minimum qualifications for licensure [36] .
Chiropractors have developed many specialties related to clinical practice. Many of these specialties began during the 1930s through 1960s. Chiropractic specialties that are common today, such as radiology and orthopedics, began as lengthy specialty curricula offered after one graduated from chiropractic college [37] .Additional specialty programs, such as sports,nutrition, and pediatrics, began later. Today,many specialty programs are available,including topic areas such as rehabilitation,sports medicine, nutrition, pediatrics, geriatrics,women’s health, radiology, and others.
Early attempts at research were mainly descriptive reports of human anatomy and physiology [16] . However, as the scientific method became an accepted practice in science,chiropractors adopted this approach to research [38] .However, continued improvements in chiropractic education and frequent distractions to battle organized medicine hampered early development of chiropractic research. Through 1960s, some groups of chiropractors that practiced certain kinds of chiropractic treatment and diagnostic procedures made observations of patient presentations and responses to treatment and communicated about their findings. For them,their observations on clinical outcomes were research [39] .
Perhaps the largest attempt to conduct observational research in the 1930s through 1950s were the efforts of BJ Palmer. BJ Palmer was the son of DD Palmer and eventually became the owner of the Palmer School of Chiropractic (now the Palmer College of Chiropractic). In his research clinic, to avoid criticism that improvement under chiropractic care following unsuccessful medical treatment did not represent misdiagnosis by chiropractors,Palmer was said to have medical doctors evaluate the patients before and after care [39] .Hundreds of thousands of dollars were invested in this lengthy effort that included records of thousands of patients [40] . The level of reporting of methodologies for this observational data was superior to many other efforts of the period.Palmer referred to the studies as “controlled”,likely due to the inclusion of medical verification of patient outcomes, however it would be decades before controlled clinical trials, as they are known today, would be used in clinical studies [24] .
One of the chiropractic profession’s first true scientists was Henry Higley, a trained chiropractor, engineer, and mathematician [41] .Higley developed structured research programs where investigators from various chiropractic colleges would input from college clinics into a central repository [39] . The first chiropractic research publication that was widely distributed within the greater scientific community was published in 1960 [42] . Significant laboratory research in chiropractic topics began in the 1970s with the work done by Dr Chung Ha Suh,a biomechanist at the University of Colorado.Dr Suh spent many years studying the potential mechanisms behind chiropractic care and biomechanics of the spine, for which he received some of the profession’s first federal funding [43] . Also in the 1970s, fellowships and other funding for chiropractors to receive training in research methods and higher education evolved.
Despite an increase in chiropractic research and science, there were few periodicals in which a chiropractic researcher could publish a paper. That changed in the 1978 with the inaugural issue of the profession’s first peer reviewed journal, the Journal of Manipulative and Physiologic Therapeutics , b e g a n publication. Published by the National College of Chiropractic (now the National University of Health Sciences), the Journal of Manipulative and Physiologic Therapeutics was dedicated entirely to chiropractic and topics germane to chiropractic science and practice [44–45] . The Journal of Manipulative and Physiologic Therapeutics was the first chiropractic scholarly journal indexed in Index Medicus and remains the profession’s flagship scholarly peer reviewed journal [44,46] .
Within a few short years, other chiropractic journals began to be published and represented various specialties, countries, and procedures.Table 2–1 presents some of the chiropractic journals that started during this era.
Table 2–1 Chiropractic Journals that Started during 1880s–1990s
The first conference that brought chiropractic researchers together with medical, osteopathic,and other researchers was “The Research Status of Spinal Manipulative Therapy”. This conference was held by the National Institute of Neurological and Communicative Disorders and Stroke. It included interdisciplinary presentations of research papers by important spinal manipulation researchers. Chiropractic colleges began research collaborations in the 1980s. One early collaborative that focused on chiropractic research was the Pacific Consortium for Chiropractic Research.The Consortium fostered collaboration between the colleges and helped hold annual research conferences for chiropractors [46] . It was not long before scientific conferences became a regular part of chiropractic science. Publications and research conferences of the early 1990s set the stage for significant scientific growth within the profession by the year 2000.